JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year BUILDING MATERIALS, CONSTRUCTION AND PLANNING Previous Question Paper (November/December - 2020 - R16)

A good building stone must satisfy several physical, chemical, and mechanical requirements to ensure durability and structural integrity. Key requirements include:

• Strength: The stone must have high crushing strength to withstand the loads imposed by the structure, typically exceeding 100 N/mm² for heavy construction.
• Durability: It should be capable of resisting the destructive effects of weathering, such as rain, frost, temperature variations, and chemical fumes.
• Hardness: The stone must be hard enough to resist abrasive forces caused by foot traffic or friction, measured by the Mohs scale.
• Low Porosity and Absorption: A good stone should have low water absorption (ideally less than 5% by weight) to prevent moisture ingress, which leads to weathering and structural decay.
• Appearance: For facing work, the stone should have a uniform color, be free from clay holes or veins, and be capable of taking a good polish.
• Workability: The stone should be easy to dress, cut, and carve into desired shapes without excessive cost or effort.
• Specific Gravity: A high specific gravity (generally above 2.4) indicates a dense and compact stone, which is desirable for stability.
• Fire Resistance: The material should be able to withstand high temperatures without cracking or disintegrating.

The selection of stone for construction depends on specific properties that dictate its suitability for different environmental and structural conditions:

1. Crushing Strength: This is the primary structural property. Stones used for load-bearing walls or foundations must be tested for compressive strength to ensure they can safely support the intended loads without failure.
2. Water Absorption: This property indicates the porosity of the stone. High absorption leads to the retention of moisture, which can cause internal stresses during freeze-thaw cycles or facilitate the growth of vegetation and chemical decay.
3. Resistance to Weathering: Stones are exposed to atmospheric agents. A selected stone must be chemically stable and physically resistant to the expansion and contraction caused by thermal changes and acidic rain, which can cause surface spalling.
4. Hardness and Toughness: Hardness is critical for flooring and paving where abrasion occurs, while toughness is essential for stones used in road construction or areas subject to impact loads to prevent shattering.
5. Texture and Structure: The internal arrangement of grains affects the stone's strength and ease of working. A fine-grained, compact, and crystalline structure is generally preferred for durability, whereas a laminated structure might be unsuitable for heavy loads but useful for paving.